Heat exchanger structure

ABSTRACT

A heat exchanger structure includes a pipe and a flow-guiding element. The pipe internally defines a chamber, in which the flow-guiding element is disposed. The flow-guiding element includes a helical main body and a plurality of turbulence promoters radially outward extended from two opposite lateral sides of the helical main body. The turbulence promoters are independently arranged on the helical main body with free ends of the turbulence promoters contacting with an inner wall surface of the chamber, so that a fin cooling effect is produced. The turbulence promoters and the helical main body together define at least one flow-guiding section. With the helically distributed turbulence promoters of the flow-guiding element, the heat transfer ability and the thermal performance factor of both laminar and turbulent flows in the pipe can be increased to provide excellent heat transfer effect.

This application claims the priority benefit of Taiwan patentapplication number 098219888 filed on Oct. 28, 2009.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger structure, and moreparticularly to a heat exchanger structure that is able to induceswirling flow, increase turbulent intensity, and expand the range ofeffective Reynolds number enabling enhanced pipe flow heat transferability of the conventional heat exchanger internally provided with atwisted tape, so as to further upgrade the conventional smooth-surfacetwisted tape's ability in enhancing the heat transfer.

BACKGROUND OF THE INVENTION

To further upgrade the heat transfer enhancing ability and the thermalperformance factor of pipe flow, and to expand the range of Reynoldsnumber that enables effectively increased heat transfer coefficient,many ways have been developed and tried, such as dispose a twisted tapein the pipe of the heat exchanger, dispose a continuous twisted tape ina helical undulated pipe, or dispose a twisted tape in a polygonal pipe,or dispose multiple twisted tapes in one conduit.

It is found the conventional smooth-surface twisted tape is not able toincrease the heat transfer ability through increasing turbulentintensity, and the conventional smooth-surface twisted tape has arelatively small range of Reynolds number.

The Reynolds number gives a measure of the ratio of inertial force toviscous force in flowing fluid. When the Reynolds number is small, theinfluence of the viscous force on the flow field is larger than that ofthe inertial force on the flow field, the turbulence in the flow fielddue to flowing speed reduces with high viscous force, and the stablelaminar flow occurs. On the other hand, when the Reynolds number islarge, the influence of the inertial force on the flow field is largerthan that of the viscous force on the flow field, the unstable turbulentflow occurs, and any minor change in flowing speed tends to develop andintensify to form a turbulent and irregular turbulent flow field.

FIG. 1 shows a heat exchanger pipe 2 that has a conventionalsmooth-surface twisted tape 1 disposed therein for the purpose ofinducing a swirling flow 3 in the pipe 2 to thereby provide heattransfer coefficient to the flow field in the pipe.

The swirling flow 3 induced by the conventional smooth-surface twistedtape 1 provides a fluid momentum perpendicular to an inner wall surfaceof the pipe 2, and can therefore better enhance the heat transfer in thelaminar region in the flow field. However, in the turbulent region,since the fluid has oscillation phenomenon, it already has a fluidmomentum perpendicular to the inner wall surface of the pipe 2. Thus,the conventional smooth-surface twisted tape 1 has relatively weakeffect on enhancing the heat transfer in the turbulent flow.

It is therefore tried by the inventor to develop an improved heatexchanger structure to solve the problems and drawbacks in theconventional heat exchanger with the smooth-surface twisted tape.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a heat exchangerstructure that is able to increase the heat transfer ability and thethermal performance factor of both the laminar flow and turbulent flowin the heat exchanger pipe.

To achieve the above and other objects, the heat exchanger structureaccording to the present invention includes a pipe and a flow-guidingelement. The pipe internally defines a chamber, in which theflow-guiding element is disposed. The flow-guiding element includes ahelical main body and a plurality of turbulence promoters radiallyoutward extended from two opposite lateral sides of the helical mainbody. The turbulence promoters are independently arranged on the helicalmain body with free ends of the turbulence promoters contacting with aninner wall surface of the chamber, so that a fin cooling effect can beproduced. The turbulence promoters and the helical main body togetherdefine at least one flow-guiding section in the chamber of the pipe.With the helically distributed turbulence promoters of the flow-guidingelement, the heat transfer ability and the thermal performance factor ofboth laminar and turbulent flows in the pipe can be increased to provideexcellent heat transfer effect. Therefore, the present inventionprovides the following advantages:

-   1. Increases the heat transfer ability and the thermal performance    factor of both the laminar and turbulent flows in the pipe.-   2. Expands the range of effective Reynolds number that enables    enhanced heat transfer effect.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and the technical means adopted by the present inventionto achieve the above and other objects can be best understood byreferring to the following detailed description of the preferredembodiments and the accompanying drawings, wherein

FIG. 1 is a cutaway view of a conventional heat exchanger;

FIG. 2 is an exploded perspective view of a heat exchanger structureaccording to an embodiment of the present invention;

FIG. 2 a is an enlarged view of the circled area 2 a of FIG. 2 showing afirst embodiment of the flow-guiding element included in the presentinvention;

FIG. 2 b is a fragmentary perspective view showing a second embodimentof the flow-guiding element included in the present invention;

FIG. 2 c is a fragmentary perspective view showing a third embodiment ofthe flow-guiding element included in the present invention;

FIG. 3 is a cutaway view of the heat exchanger structure of the presentinvention; and

FIG. 4 is a cutaway view showing the flow direction of the fluid in theheat exchanger pipe of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer to FIGS. 2, 2 a-c, 3 and 4. As shown, the heat exchangerstructure according to the present invention includes a pipe 4 and aflow-guiding element 5.

The pipe 4 internally defines a chamber 41.

The flow-guiding element 5 is disposed in the chamber 41, and includes ahelical main body 51. A plurality of turbulence promoters 52 is radiallyoutward extended from two opposite lateral sides of the helical mainbody 51. The turbulence promoters 52 are arranged independently. Each ofthe turbulence promoters 52 has a free end 521 facing toward an innerwall surface of the chamber 41. The turbulence promoters 52 and thehelical main body 51 together define at least one flow-guiding section53.

The pipe 4 has at least one inlet end 42 and at least one outlet end 43.A fluid 6 enters the chamber 41 of the pipe 4 via the inlet end 42.

The flow-guiding element 5 is disposed in the chamber 41 of the pipe 4with the free ends of the turbulence promoters 52 of the flow-guidingelement 5 in contact with the inner wall surface of the chamber 41, suchthat the turbulence promoters 52 and the chamber 41 together define ahelical flow path 44 in the pipe 4. The fluid 6 flows through thehelical flow path 44 to induce a swirling flow, which provides heattransfer coefficient to the flow field in the pipe 4.

Due to an increased torsion of the main body 51 and the turbulencepromoters 52 of the flow-guiding element 5, the range of effectiveReynolds number enabling upgraded heat conduction is increased.

The turbulence promoters 52 each can be in the form of a plate, a needle(not shown), a bar, or a strip (not shown). In the illustratedembodiment of the present invention, the turbulence promoters 52 are inthe form of plates, as can be seen from FIG. 2 a. However, it isunderstood the turbulence promoters 52 are not limited to the form ofplates, but can be in other forms.

The turbulence promoters 52 are spaced from one another by a clearance522. The turbulence promoters 52 can have the same length, as shown inFIG. 2 a, or have different lengths, as shown in FIG. 2 b. Further, theturbulence promoters 52 can be spaced from one another by a uniformclearance 522, as shown in FIG. 2 a, or by different clearances 522, asshown in FIG. 2 c.

Please refer to FIG. 4. The flow-guiding element 5 is disposed in thechamber 41 of the pipe 4; the fluid 6 flows into the pipe 4 via theinlet end 42 and out of the pipe 4 via the outlet end 43 to conduct heatexchange. When the fluid 6 enters the chamber 41 of the pipe 4 via theinlet end 42, the helically distributed turbulence promoters 52 of theflow-guiding element 5 enable a shear stress layer formed behind theturbulence promoters 52 to interact with the swirling flow in the mainflow field, so that the fluid 6 has increased fluid mixing property andturbulent intensity, which leads to enhanced heat transfer ability andincreased pressure loss coefficient. Compared to the average Nusseltnumber of the conventional smooth-surface twisted-tape tube that isabout 1.28-2.4 times as high as the smooth-surface round pipe, theturbulence promoters 52 of the flow-guiding element 5 of the presentinvention has increased average Nusselt number and heat transfercoefficient in laminar region that is 6.3-9.5 times as high as that ofthe smooth-surface round pipe.

Further, with the flow-guiding element 5 of the present invention, therange of effective Reynolds number enabling upgraded heat transfer iswider than that of the conventional continuous smooth-surface twistedtape. Meanwhile, the flow-guiding element 5 has increased torsion tothereby lead to an increased range of effective Reynolds number enablingenhanced heat transfer.

Moreover, from the analysis result that Fanning pressure losscoefficient changes with the Reynolds number, it is concluded that theflow-guiding element 5 of the present invention is able to suppress theconversion of the flow field from the laminar flow into the turbulentflow in the transition region.

The turbulence promoters 52 of the flow-guiding element 5 are sodesigned that they not only provide higher heat transfer enhancing valuethan the conventional continuous smooth-surface twisted tape, but alsoenable improved thermal performance factor.

In the illustrated embodiment of the present invention, the heattransfer ability and the thermal performance factor of thesmooth-surface round pipe is increased while only one singleflow-guiding element 5 is provided. It is trusted the heat transferability and the thermal performance factor of the smooth-surface roundpipe can be further increased when more flow-guiding elements 5 areprovided (not shown). Moreover, when the torsion for the flow-guidingelement 5 is properly selected, it would be able to simultaneouslyincrease the heat transfer ability and the thermal performance factor ofboth the laminar and turbulent pipe flows.

The present invention has been described with some preferred embodimentsthereof and it is understood that many changes and modifications in thedescribed embodiments, such as any change in the configuration orarrangement of the pipe or the flow-guiding element, can be carried outwithout departing from the scope and the spirit of the invention that isintended to be limited only by the appended claims.

1. A heat exchanger structure, comprising: a pipe internally defining achamber; and a flow-guiding element being disposed in the chamber; theflow-guiding element including a helical main body and a plurality ofturbulence promoters radially outward extended from two opposite lateralsides of the helical main body; the turbulence promoters beingindependently arranged, and each having a free end facing toward andcontacting with an inner wall surface of the chamber; and the turbulencepromoters and the helical main body together defining at least oneflow-guiding section.
 2. The heat exchanger structure as claimed inclaim 1, wherein the turbulence promoters are selected from the groupconsisting of plate-shaped, needle-shaped, bar-shaped, and strip-shapedturbulence promoters.
 3. The heat exchanger structure as claimed inclaim 1, wherein the flow-guiding element and the chamber togetherdefine a helical flow path in the pipe.
 4. The heat exchanger structureas claimed in claim 1, wherein the turbulence promoters are spaced fromone another by a clearance.
 5. The heat exchanger structure as claimedin claim 1, wherein the turbulence promoters are the same in length. 6.The heat exchanger structure as claimed in claim 1, wherein theturbulence promoters are different in length.
 7. The heat exchangerstructure as claimed in claim 1, wherein the turbulence promoters arespaced from one another by a uniform clearance.
 8. The heat exchangerstructure as claimed in claim 1, wherein the turbulence promoters arespaced from one another by different clearances.